What does "I'll do, I'll do, and I'll do" mean?

Question

In Macbeth, while the witches are having their little meeting before going to meet Macbeth and tell him that he's going to be king, one of the witches details her plan of revenge against a greedy "rump-fed ronyon":

Third Witch
Sister, where thou?
First Witch
A sailor's wife had chestnuts in her lap,
And mounch'd, and mounch'd, and mounch'd. "Give me," quoth I:
"Aroint thee, witch!" the rump-fed ronyon cries.
Her husband's to Aleppo gone, master o' the Tiger;
But in a sieve I'll thither sail,
And, like a rat without a tail,
I'll do, I'll do, and I'll do.
_{Macbeth, Act 1, Scene 3, Amsco Literature Program edition}

What does "I'll do, I'll do, and I'll do" at the end there mean? Are each of those referring to different acts, which the "and" would seem to indicate? If not, why is it repeated three times? What is the "I'll do" referring to that she's going to, well, do?

Answer 1

Not all editors explain "I'll do" and the explanations aren't always the same.

The edition by Barbara A. Mowat and Paul Werstine (Folger Shakespeare Library, 2003, page 14) has a gloss saying that "like" (in the preceding line) means "in the form of" but has nothing for "I'll do".

The edition by Burton Raffel (The Annotated Shakespeare, Yale University Press, 2005, page 11) merely says that the line is "intoned, with a gleeful malice" but lets the reader guess the meaning.

The edition by G. K. Hunter (New Penguin Shakespeare (Penguin, 1967, page 141) has the following gloss for "do":

as in the modern vague abusive 'I'll do him' = 'I'll cause him harm'.

The edition by John Dover Wilson (The New Shakespeare, Cambridge University Press, 1947, page 100) has the following endnote for "do":

Most edd. assumes that she gnaws a hole in the hull. But this contradicts l. 24. What she will 'do' is left mysterious, until she unfolds her scheme of making 'the voyage one long torture' (K.).

("K." refers to G. L. Kittredge's edition.)

The edition by Jonathan Bate and Erik Rasmussen (The RSC Shakespeare, Macmillan, 2009, page 27) has the following gloss for "do":

act/have sex (it was thought that witches often seduced their male victims)

The edition by Nicholas Brooke (The Oxford Shakespeare, Oxford University Press, 1999, page 101) does not gloss "do" but tells us the following about "rat without a tail":

Steevens (1793) stated that old writers rationalized defective transformation by claiming that no part of a women could be changed into a tail, but he cites no authority. Thomas (p. 529) states that allusions to animal transformation are rare.

("Steevens" refers to George Steevens, who published a variorum edition of Shakespeare's plays in the 1790s. "Thomas" is a reference to Religion and the Decline of Magic (1971) by Keith Thomas, which is something of a classic on popular beliefs in sixteenth- and seventeenth-century England.)

Kenneth Muir (Arden Shakespeare, Routledge, 1984, page 12) prefers the explanation given in Witchcraft in Old and New England (1929) by G. L. Kittredge, who wrote that

she will take the shape of a rat in order to slip on board the Tiger unnoticed. This, and not to use her teeth, is the object of the transformation. There she will bewitch the craft and lay a spell upon the captain. There is no question of scuttling the ship.

A. R. Braunmuller (The New Cambridge Shakespeare, Cambridge University Press, 1997, page 110) glosses "do" as "act; fornicate" and adds the following quote from Frances Dolan's book Dangerous Familiars: Representations of Domestic Crime in England 1550–1700 (1994, page 212):

Many dramatizations of witches as powerful, dangerous agents associate their agency with female sexual desire.

Robert S. Miola's edition (Norton Critical Editions. W. W. Norton, 2014, page 7) has the following gloss for "do":

(1) act; (2) have sexual intercourse.

In short, editors don't fully agree about what the weird sister will "do". Glosses suggesting a sexual meaning are limited to relatively recent editions (Braunmuller, Miola, Bate & Rasmussen), almost as if older editions were too "Victorian" to mention that.

However, the first weird sister's (or the first witch's) next speech explains what she'll do. First, she'll make sure that the ship will endure many storms without perishing. Second, she "will drain [the sailor] dry as hay", which seems to justify the sexual explanation of "do".

The threefold repetition is part of a pattern in the play: three witches, three murderers of Banquo, "Thrice to thine and thrice to mine, ..." (in Act I, scene 3), "Had I three ears" (in Act 4, scene 1), etcetera.

Answer 2

The note of Steevens mentioned in the other answer reads as follows:

It should be remembered (as it was the belief of the times), that though a witch could assume the form of any animal she pleased, the tail would still be wanting.

The reason given by some of the old writers, for such a deficiency, is, that though the hands and feet, by an easy change, might be converted into the four paws of a beast, there was still no part about a woman which corresponded with the length of tail common to almost all four-footed creatures.

_{George Steevens (1793). Macbeth, note to 1.3.8. In The Plays of William Shakespeare, volume 7 page 343. London: T. Longman, etc.}

Steevens does not name the “old writers” in this note. In other notes on the scene he mentions Reginald Scot’s Discoverie of Witchcraft (1584) and the anonymous Damnable Life of Doctor Fian (1592). Neither of these mentions the difficulty with the tail, so I do not know whence he got this detail.

Some other notes on the line:

She threatens in the shape of a rat to gnaw through the hull of the Tiger and make her spring a leak.

_{W. G. Clark and W. A. Wright, eds. (1869). Macbeth, note to 1.3.10. Oxford: Clarendon.}

The Note to this passage in one of the Modern Editions of Shakspere, is, “She threatens in the shape of a rat to gnaw through the hull of the Tiger, and make her spring a leak.” But, in our opinion, this was what, in her fiendish vindicativeness, the Witch never dreamt of doing. It was evidently to the destruction of the Tiger’s rudder that she intended to apply her energies; and this view accepted, “the Pilot's Thumb,” that ghastly treasure, takes an appropriate and strange significance. Had the Tiger sprung a leak, she would have gone down, and “there an end on’t,” but she was to be knocked about, the sport of the elements, for more than a year and a half, unable to sink, and probably not to be lost in the end, but to strand on some unknown shore far from the many-mosqued City, or to drift, with her companionless and skeleton-like skipper, into her own bay:

“Oh! dream of joy! is this indeed
The light-house top I see?
Is this the hill? is this the kirk?
Is this mine own Countree?Ӡ

In the eight lines in this scene, commencing, “I’ll drain him dry as Hay,” we seem, indeed, to have the reef, out of which grew “The Rime of the Ancient Mariner.”‡

_{Allan Park Paton, ed. (1877). Macbeth, note to 1.3.8–10. Edinburgh: Edmonston.}

_{† Samuel Taylor Coleridge (1798). ‘The Rime of the Ancient Mariner’. In Lyrical Ballads, page 39. London: J. & A. Arch. ‡ This conjecture seems very unlikely in light of the similarities of Coleridge’s poem to The Strange and Dangerous Voyage of Captain Thomas James (1633), described by Ivor James in The Source of the Ancient Mariner (1890).}

My own opinion is that (as shown by the multiplicity of speculations) we can’t expect to pin down the meaning precisely. The witch proposes to carry out some acts of malice, the specifics of which are left to our imagination.